This invention is generally directed to a novel temperature indicator for providing a visual indication to an operator of when a vehicle axle, such as a trailer axle, filled with a semi-fluid synthetic grease for lubricating the wheel bearings therein has achieved an unsafe temperature. More particularly, one form of the present invention is directed to a novel temperature indicator that can be retrofit into existing vehicle axles without modification of the design of the axle.
Current trailer hub/bearing designs have moved towards using a semi-fluid synthetic grease lubricant for lubricating the wheel bearings instead of gear oil as had commonly been used in prior trailer hub/bearing designs. Semi-fluid synthetic grease is more advantageous because it is not as sensitive to a less than perfect wheel seal and therefore, leakage is less likely that with an oil filled axle hub.
When leakage occurs with an oil filled axle hub, the oil spreads or sprays around the axle, saturating everything in the area. This can result in a fire from hot brake shoes and drums that become coated with oil if a seals fails.
When leakage occurs with a semi-fluid synthetic grease filled axle hub, because the semi-fluid synthetic grease is more solid than oil, the semi-fluid synthetic grease does not spread or spray around the axle like oil. The semi-fluid synthetic grease merely pushes out past the seal and either falls away cleanly, or just stays present around the immediate area, thereby preventing fires.
An advantage of using an oil filled axle hub is that such hubs were easy to monitor with a window in the hub cap that had a fill line. If the user found that the oil was low (i.e., below the fill line), a plug was simply pulled on the hub cap and oil was added until the level reached the fill line.
With a semi-fluid synthetic grease filled axle hub, however, the semi-fluid synthetic grease does not flow through the bearings, but tends to stay in the grease chamber in the hub even when the wheel stops. This occurs especially in cool weather since the semi-fluid synthetic grease is used. At low temperatures, the viscosity of the semi-fluid synthetic grease is heavy like a grease, but at higher temperatures, the semi-fluid synthetic grease starts to flow more like a heavy liquid.
Because of this characteristic of the semi-fluid synthetic grease, a hub cap without a window is used to prevent the mechanic from mistakenly thinking that the hub was low on oil since the oil level would not show up in the window. Because the window used with oil does not work with a semi-fluid synthetic grease filled hub, usually a simple metal or solid plastic cap is employed. The problem that results is that the mechanic cannot monitor the axle to determine whether an adequate amount of lubrication is present. It is well know that if a wheel bearing is operated for a long time without adequate lubrication, the bearing will heat up significantly and cause the hub to also heat up since the bearings press into the wheel/hub. This can result in a catastrophic bearing failure if this condition is left undetected.
The present invention presents a novel temperature indicator for providing a visual indication to an operator of when a vehicle axle, such as a trailer axle, filled with a semi-fluid synthetic grease for lubricating the wheel bearings therein has achieved an unsafe temperature. One form of the temperature indicator of the present invention can be easily retrofit into existing trailers, without modification of the trailer. Other features and advantages of the present invention will become apparent upon a reading of the attached specification, in combination with a study of the drawings.